PROLOG This manual page is part of the POSIX Programmer
s Manual. The Linux implementation of this interface may
differ (consult the corresponding Linux manual page for
details of Linux behavior), or the interface may not be
implemented on Linux.

DESCRIPTION These functions shall compute the principal
value of the arc cosine of their argument x. The value of x
should be in the range [-1,1].

An application wishing to check for error situations
should set errno to zero and call
feclearexcept(FE_ALL_EXCEPT) before calling these functions.
On return, if errno is non-zero or fetestexcept(FE_INVALID |
FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an
error has occurred.

RETURN VALUE Upon successful completion, these functions
shall return the arc cosine of x, in the range [0,pi]
radians.

For finite values of x not in the range [-1,1], a domain
error shall occur, and either a NaN (if supported), or an
implementation-defined value shall be returned.

If x is NaN, a NaN shall be returned.

If x is +1, +0 shall be returned.

If x is ±Inf, a domain error shall occur, and
either a NaN (if sup- ported), or an implementation-defined
value shall be returned.

ERRORS These functions shall fail if:

Domain Error The x argument is finite and is not in the
range [-1,1], or is ±Inf.

If the integer expression (math_errhandling &
MATH_ERRNO) is non-zero, then errno shall be set to [EDOM].
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, then the invalid floating-point
exception shall be raised.

The following sections are informative.

EXAMPLES None.

APPLICATION USAGE On error, the expressions
(math_errhandling & MATH_ERRNO) and (math_errhandling
& MATH_ERREXCEPT) are independent of each other, but at
least one of them must be non-zero.

COPYRIGHT Portions of this text are reprinted and
reproduced in electronic form from IEEE Std 1003.1, 2003
Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the
Institute of Electrical and Electronics Engineers, Inc and
The Open Group. In the event of any discrepancy between this
version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .